1. Field of the Invention
The present invention relates to a drive system designed to transfer power from a power source onto a plurality of drivetrains.
2. Description of the Related Art
Many industrial drive system concepts are based on the distribution and transfer of power, originating from a power source onto several power consumers, which are positioned downstream of the power consumer. A significant area of application of such a drive system concept are roll mills. The power developed by a motor is transferred via drivetrains onto several working rolls. For that purpose, a transfer gearbox is connected ahead of the drivetrains. The transfer gearbox includes in its simplest form only several spur gears, which are positioned in a manner that allows the transfer of power onto the downstream positioned universal drivetrains in accordance to the ratio of the spur gears. The drivetrain can further include apparatuses for torque and speed amplification. Disturbances on the driven equipment cause an interruption of the torque transfer from the driving to the driven system, resulting in an unacceptable increase in torque. In roll mills, these types of disturbances manifest themselves as jams during the rolling process. The cause of such jams is primarily a result of a lamination of the rolling stock, the use of cold rolling stock, or a fracture of the roll. The reason for such an unacceptable increase in torque is the continued propulsion of the masses in spite of the disturbances on the driven side of the drivetrain. This manifests itself in a deformation of the drivetrain, which can lead to torsional fractures in extreme cases. In order to avoid such failures, as well as prevent the unacceptable torque increase, special and quickly separable safety couplings are available for the transfer of torque between two mechanical components on the same axis. An exemplification of such a coupling, including an overload safety device, designed to prevent excessive torque spikes, is published in the German paper DE-OS-29-23-902. The coupling includes at least one thin-walled sleeve, forming a wall of a ring-shaped chamber extending in axial direction. The ring-shaped chamber can be pressurized with a medium in order to elastically deform the sleeve in radial direction causing it to jam against the surface of an element onto which the coupling is mounted. Adjacent to the ring-shaped chamber are drillings, which are a part of a safety or coupling relief device. As a result of the relative motion between the surfaces and the actions of the relief device, the pressurized medium residing in the ring-shaped chamber can escape through the drillings, thus lowering the pressure inside the chamber.
To transfer a certain torque level, a certain surface pressure is required. For that purpose, oil is pumped into the chamber, which is needed to deform the respective machine components relative to one another. In this way, the coupling is adjusted to the desired torque capacity. If, during an overload condition, this torque is exceeded, the coupling slips. The maximum torque level that can be transmitted reduces because the effective, static friction coefficient transitions into the sliding friction coefficient. There is a relative motion in circumferential direction between the individual elements of the two machine components, which are jammed relative to one another. A shear disk mounted on one machine component shears off a shear valve, opening the connection to the ring-shaped chamber of the coupling. After shearing off the shearing valve (or valves), the pressurized oil can freely expand and the torque to be transmitted reduces to zero within a few milliseconds. Such couplings are placed in a sensible manner in areas of possible disturbances.
For an application in a roll mill, the safety coupling must be positioned near the rolls. This, however, is not always feasible, which is why such a safety coupling must be mounted either in every universal drivetrain or immediately ahead of every universal drivetrain. This disadvantage of such an arrangement of safety couplings in a drivetrain, especially in an application such as a roll mill, is the high cost, since every universal drivetrain or branch of a power take-off is assigned a safety coupling. Furthermore, there is a direct relationship between the size of the safety coupling and the torque to be transmitted. Higher torque levels require a larger diameter safety coupling, which is met by limitations as a result of the placement of the universal drivetrains or the individual power take-offs, as well as their center-line distances to one another.